The overall objective of the proposed research is to understand that mechanism of motor control which pre-programs the final position of a movement. The main experimental focus will require human subjects to make extensions and flexions of the forearm or to maintain the arm at a fixed position. Usually, but not always, the arm pointing will be done to a visual target, but without sight of the limb. External forces will be added during some conditions. Experiments will be controlled by a PDP-11 with on-line measurement of arm trajectory, timing of visual stimuli, external force, and electromyographic (EMG) activity of biceps and triceps as recorded from surface electrodes. Velocity, acceleration, integrated EMGs, error in position, etc. will also be calculated. The research plan contains two parts, both linked by a theoretical framework for the pre-programming of final position. The first part of the research plan outlines a set of experiments designed to find experimental and theoretical quantitative relationships between the EMG activities of the flexors and extensors for the elbow joint; the biomechanical properties of these muscles; external forces; and the final position of the forearm. The second part of the research concerns the accuracy and consistency of pre-programmed movements, both with regard to final position as well as overall muscle tension, with the aim of analyzing the factors that contribute noise to the system.